For any [Operating System Environment (OSE)] in which you use Running Instances of the server software, you may use up to the same number of passive fail-over Running Instances in a separate OSE on any Server for temporary support
COLD Data Center

You can build the machines with the, say Exchange. Switch it off.

You can periodically update it with data, although strictly speaking it is not supposed to be one way replicating all of the time. I think with the latest rules change, this is once every 90 days for data and testing…

Also under these rules, the systems needs to go back to the primary machines once the effected machines are restored, and these DR units turned off once more.
If they exist in an active – active state, yes.

DR Applications servers with SA in a cold state (Exchange, Sharepoint, SQL etc). No